The present invention relates to a process for producing a decorative sheet or plate having a concave pattern which is in coincidence with a design or color pattern.
Several methods of forming concavities and especially concavities coincidently matching printed patterns on thermosetting resin decorative sheets such as melamine decorative sheet and diallyl phthalate decorative sheet have been known. One method uses a printing step wherein the coincident matching of the portions for producing concavities with other pattern portions can be conducted in the printing step. Moreover, this method using a printing step is industrially advantageous in that the ordinary processing steps can be substantially applied after the printing step, in comparison with other methods such as a method using a mold or the like which has a surface structure in conformity with the printed pattern.
One method for forming concavities, using a printing step, for producing coincidently embossed concave-convex decorative sheets is set out in Japanese Patent Laid-Open Application No. 111554/1979. This method is characterized by the steps of forming an ordinary printed layer of a desired design pattern with an ordinary printing ink on a paper for decorative use; forming thereon a foamable printed layer having a desired pattern with a heat-foamable printing ink; impregnating the decorative paper on which the above mentioned two printed layers have been formed with a thermosetting resin and drying the printed paper to form an impregnated paper; laminating the impregnated paper on a substrate; and then subjecting the laminate to a molding treatment by heating and pressing. During the molding by heating and pressing, the foamable printed layer undergoes foaming, and poor setting occurs in the thermosetting resin around the foamed portions. As a result, when a mirror plate used upon heating and pressing is peeled off, the poorly set portions sticking to the mirror plate are removed to form concavities coincident with the printed pattern.
However, there are some problems in this process. The concavities formed according to the above described process are produced because of the failure in cohesion due to the decrease in cohesion strength in the poorly thermoset resin and the foamed portions. Such failure in cohesion is rather accidental, but the result is that distinct concavities corresponding to the foamed printed layer cannot always be formed and only mat portions may be formed. Another, problem with this process develops when the stained mirror plate is repeatedly used for the step of molding by heating and pressing, in that the uncured resin adheres to the mirror plate, and thus a decorative sheet product having uneven gloss surface may be produced.
An object of the present invention is to provide a process for producing a thermosetting resin decorative sheet having distinct concavities in coincidence with a printed pattern by eliminating the above described problems that occur in the conventional processes for production of thermosetting resin decorative sheets.